Local anesthetic patches such as lidocaine are widely used for the purpose of removing a pain which is caused upon puncture. Particularly, local anesthetic patches find widespread use in hemodialysis. Hemodialysis patients are treated with dialysis three times a week, for example, by having two dialysis needles, each having a diameter ranging from 17 to 18 G (gauge), inserted through their skin for an extracorporeal blood circulation to remove waste materials from the blood. Such local anesthetic patches are used to remove the pain caused upon puncture.
Lidocaine patches take a long time, e.g., 2 hours, prior to the onset of their effect. Therefore, the skin area to which a lidocaine patch is applied is likely to be irritated. In addition, the efficacy of lidocaine patches tends to be insufficient because they fail to deliver the drug deeply into the tissue.
On the other hand, iontophoresis is advantageous in that it takes a shorter time until the onset of the drug efficacy and it can deliver the drug more deeply into the tissue. The above problems can be solved by combining local anesthetic patches such as lidocaine with iontophoresis. Specifically, iontophoresis refers to a process wherein positive and negative electrodes are placed at two spaced points on a skin and an electric current is passed from one of the electrodes across the stratum corneum to the other electrode thereby to move a charged drug based on the principle of electrophoresis for facilitating transdermal drug absorption. Iontophoresis provides a basis for a transdermal drug administration system. Usually, one of the positive and negative electrodes is held in contact with a gel containing the drug and referred to as a donor portion, and the other electrode is held in contact with a gel containing salt solution and referred to as a reference portion.
According to iontophoresis, the charged drug is subjected to facilitation of absorption in principle. There has been a report stating that since a water flow is developed in the patient's body due to an electric current, even a non-charged drug or even a high-molecular-weight drug exhibits increased skin permeability.
Japanese Laid-Open Patent Publication No. 2007-532193 (PCT) discloses an electrically assisted delivery device utilizing iontophoresis which includes an electrode assembly having positive and negative electrodes containing a drug and a controller for supplying an electric current to the electrode assembly. The disclosed electrically assisted delivery device is problematic in that it is not small enough to make the controller integral with a patch and is highly costly.
Japanese Laid-Open Patent Publication No. 09-510387 (PCT) discloses an electrically operated administration device having a structure wherein a flexible substrate and a button cell for energizing a pair of electrode means to be applied to the skin of a patient are disposed on upper portions of the electrode means.